When a food product containing water is packed in a tray and displayed at a store front or the like at low temperature with a surface of the tray wrapped with a plastic film, fog grows on the plastic film on the side facing the food product particularly in a case where the food product is a high water-containing product. This is a result of fog generation on the inner surface of the wrapping film facing the food product due to aggregation of tiny water vapors. Invisibility of the contents of the wrapped products through the wrapping film falls into disfavor with consumers. Various attempts have been proposed in order to prevent fog generation on a plastic film on the side facing a food product.
Japanese Unexamined Patent Application Publication No. 2002-240214 proposes a sealant film having an excellent antifogging property in which a ketonic compound layer of an ethylene-vinyl acetate copolymer and/or a polyamide-based resin layer are laminated in accordance with a co-extrusion method on one surface of a polyolefin-based resin layer containing an antifog agent with a modified polyolefin-based resin layer interposed in between.
However, when the film using the antifog agent is an antifogging film having a printed surface on an outer layer, the antifogging effect may be lost if the printed film is rolled and stored. When the film is rolled on a spindle of a core material after printing on the film, the printed surface and a surface on an inner layer of the film subjected to an antifogging treatment are brought into contact with each other at a high pressure. Moreover, storage of the film in the state of being wound into the roll causes degradation in the antifogging property of the film attributable to the strong contact between the printed surface on the outer layer and the surface of the inner layer subjected to the antifogging treatment. This degradation in the antifogging property is considered as being due to partial transition of the antifog agent to the outer layer or into components of printing ink.
U.S. Pat. No. 6,677,014 proposes a plastic antifogging film having a first side and a second side in which at least the first side of the antifogging film has an antifogging property and at least part of the second side has a printed image, the printed image being formed of an effective amount of cellulose acetyl propionate including an average propionyl content ranges from about 35 wt % to 55 wt %, an average acetyl content ranges from about 0.3 wt % to 3 wt %, and an average hydroxyl content ranges from about 1 wt % to 10 wt % on the basis of the cellulose acetyl propionate; i.e., the use of printing ink containing specific components. Although these techniques exert an antifogging effect to some extent, there is a demand for development of a technique that can maintain an antifogging property more effectively.
An object of the present invention is to provide an antifog laminated film in which occurrence of degradation in an antifogging property can be reduced even when there is a strong contact between a surface subjected to an antifogging treatment and a printed surface of the antifog laminated film having a printed outer layer due to an operation of winding the film into a roll and the like.